Develop Reference

SQL Server cannot build connection string to db

I tried the following in SQL Server Management Studio; I can connect and run query, but not from my project
string s = "Server=LAPTOP-7J47C5JA\SQLEXPRESS;Database=Test;Trusted_Connection=True;";
string queryString = "SELECT * from tbclienti";
cn = new SQLConnection(s);
// Create the Command and Parameter objects.
SqlCommand command = new SqlCommand(queryString, cn);
cn.Open();
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Text = reader[0].ToString();
label1.Text = reader[1].ToString()+ " " + reader[2].ToString();
}
reader.Close();
cn.Close();

I posted here whole code what could look like. Try it now.
string s = #"Server=(local)\SQLEXPRESS;Database=Test;Integrated Security=SSPI;";
using(SqlConnection cn = new SqlConnection(s))
{
string queryString = "SELECT * from tbclienti";
try
{
cn.Open();
// Create the Command and Parameter objects.
SqlCommand command = new SqlCommand(queryString, cn);
SqlDataReader reader = command.ExecuteReader();
while (reader.Read())
{
Text = reader[0].ToString();
label1.Text = reader[1].ToString()+ " " + reader[2].ToString();
}
reader.Close();
}
catch(Exception ex)
{
// see if error appear
}
finally
{
cn.Close();
}
}

Exception: Invalid attempt to Read when reader is closed

I am trying to update my database while reading data from it, but the reader gets closed and it throws the exception that it can''t read wen reader is closed. Is the update.ExecuteNonQuery() closing the reader method?
If i get rid of linescon.Close(); con.Open(); i get There is already an open DataReader associated with this Connection which must be closed first.
So how can i update my database records while keep the reading opened?
{
public class MySqlReadUpdate
{
public int Id { get; set; }
public string Notes { get; set; }
}
static void Main()
{
List<MySqlReadUpdate> dbData = new List<MySqlReadUpdate>();
var config = "server=localhost;user id=root; database=restaurants; pooling=false;SslMode=none;Pooling=True";
MySqlConnection con = new MySqlConnection(config);
MySqlDataReader reader = null;
string query = "SELECT id, notes FROM customers";
MySqlCommand command = new MySqlCommand(query, con);
con.Open();
reader = command.ExecuteReader();
while (reader.Read())
{
MySqlReadUpdate newMySqlReadUpdate = new MySqlReadUpdate();
newMySqlReadUpdate.Id = (int)reader["id"];
newMySqlReadUpdate.Notes = (string)reader["notes"];
string note = newMySqlReadUpdate.Notes;
var notesplit = note.Split(' ', '\n')[1];
dbData.Add(newMySqlReadUpdate);
Console.WriteLine(newMySqlReadUpdate.Id);
Console.WriteLine(newMySqlReadUpdate.Notes);
Console.WriteLine(note);
Console.WriteLine(notesplit);
con.Close();
con.Open();
string query2 = "UPDATE customers SET notes='" + notesplit + "' WHERE id='" + newMySqlReadUpdate.Id + "';";
MySqlCommand update = new MySqlCommand(query2, con);
update.ExecuteNonQuery();
}
con.Close();
Console.WriteLine("Finished!");
Console.Read();
}
}
}

You cannot close a connection like you are, because the data reader depends on it. Once you call con.Close you break it. That's why you see an exception the next time it gets to reader.Read().
What you want is to add MultipleActiveResultSets=True in the configuration string; however, as we discussed in the comments it's apparently still not supported in MySQL. Therefore, the answer is two connection instances.
List<MySqlReadUpdate> dbData = new List<MySqlReadUpdate>();
var config = "server=localhost;user id=root;database=restaurants;pooling=false;SslMode=none";
MySqlConnection con = new MySqlConnection(config);
MySqlConnection cmdCon = new MySqlConnection(config);
MySqlDataReader reader = null;
string query = "SELECT id, notes FROM customers";
MySqlCommand command = new MySqlCommand(query, con);
con.Open();
cmdCon.Open();
reader = command.ExecuteReader();
while (reader.Read())
{
MySqlReadUpdate newMySqlReadUpdate = new MySqlReadUpdate();
newMySqlReadUpdate.Id = (int)reader["id"];
newMySqlReadUpdate.Notes = (string)reader["notes"];
string note = newMySqlReadUpdate.Notes;
var notesplit = note.Split(' ', '\n')[1];
dbData.Add(newMySqlReadUpdate);
Console.WriteLine(newMySqlReadUpdate.Id);
Console.WriteLine(newMySqlReadUpdate.Notes);
Console.WriteLine(note);
Console.WriteLine(notesplit);
string query2 = "UPDATE customers SET notes='" + notesplit + "' WHERE id='" + newMySqlReadUpdate.Id + "';";
MySqlCommand update = new MySqlCommand(query2, cmdCon);
update.ExecuteNonQuery();
}
con.Close();
cmdCon.Close();
Console.WriteLine("Finished!");
Console.Read();
I would recommend that you also modify your code to use using statements or wrap things in try-finally blocks.

C# Select Transact-SQL (Table Column Property)

I wanna select Table Column property using c#. I wrote this code. My query is working on the sqlserver. But i dont get max length in c#.
My Query Is Here
//TableName:Contents, ColumnName : Title
select Col_Length('Contents','Title') as columnLengthh
Result Is Here:
My C# Code Here :
string columnLength = "select Col_Length('Contents','Title') as columnLengthh";
adapter = new SqlDataAdapter(columnLength, connection);
dataSet = new DataSet();
adapter.Fill(dataSet);
DataTable dataTable2 = dataSet.Tables[0];
foreach (DataRow row in dataTable2.Rows)
{
var x = row["columnLengthh"].ToString();
}
Result (x = -1)
How i get length in c#.
Please help!

Check your query is correct
Change the connectionString to match what you have - for example:
string connectionString = #"server=localhost\mysqlserver;database=master;Trusted_Connection=True;";
and use the following code:
string queryString = "select Col_Length('Contents','Title') as columnLengthh";
string connectionString = #"your con string";
SqlConnection connection = null;
try
{
connection = new SqlConnection(connectionString);
using (SqlCommand command = new SqlCommand(queryString, connection))
{
connection.Open();
var result = command.ExecuteScalar();
Console.WriteLine("columnLengthh = {0}", result);
}
}
catch (Exception ex)
{
ex.ToString();
}
finally
{
connection.Close();
}

Simply use the SqlConnection, SqlCommand, SqlReader etc classes to communicate to SQL Server.
string queryString = "select Col_Length('Contents','Title') as columnLengthh";
string connectionString = "Your connection string";
SqlConnection connection = null;
try
{
connection = new SqlConnection(connectionString)
using (SqlCommand command = new SqlCommand(queryString, connection)) ;
{
connection.Open();
var result = command.ExecuteScalar();
Console.WriteLine("columnLengthh = {0}", result);
}
}
finally
{
connection.Close();
}

C# use a reader in another reader solution?

I need to get some mysql data into another mysql reader request anyway to workaround that I apparently can't have 2 readers open at the same time it will all end up in a datagrid
public void DBSelectPraktikanter(object sender)
{
string Command = "SELECT * FROM forlob WHERE firmaid = N'" + firmaid + "'";
MySqlConnection sqlConnection1 = new MySqlConnection(connectionString);
MySqlCommand command = new MySqlCommand(Command, sqlConnection1);
sqlConnection1.Open();
MySqlDataReader reader = command.ExecuteReader();
var items = new List<praktikanter>();
if (reader.HasRows)
{
while (reader.Read())
{
string praktikantid = String.Format("{0}", reader["praktikantid"]);
string Command2 = "SELECT * FROM praktikanter WHERE id = N'" + praktikantid + "'";
MySqlCommand command2 = new MySqlCommand(Command, sqlConnection1);
MySqlDataReader reader2 = command.ExecuteReader();
if (reader.HasRows)
{
while (reader2.Read())
{
Praktikant = String.Format("{0}", reader["Navn"]);
}
}
string Fra = String.Format("{0}", reader["fra"]);
string Til = String.Format("{0}", reader["til"]);
items.Add(new praktikanter(Praktikant, Fra, Til));
}
}
sqlConnection1.Close();
var grid = sender as DataGrid;
grid.ItemsSource = items;
}

Instead of nesting MySqlCommands and looping the first resultset to query again the database to collect all of your data you should really use one query. Also use the using-statement to ensure that the connection gets closed even on error and use sql-parameters to avoid sql-injection issues:
var items = new List<praktikanter>();
string sql = #"SELECT p.*, f. Navn
FROM praktikanter p INNER JOIN forlob f ON p.id = f.praktikantid
WHERE f.firmaid = #firmaid";
using (var con = new MySqlConnection(connectionString))
using (var command = new MySqlCommand(sql, con))
{
command.Parameters.Add(new MySqlParameter("#firmaid", MySqlDbType.VarChar).Value = firmaid);
con.Open();
using (var rd = command.ExecuteReader())
{
while (rd.Read())
{
string praktikant = rd.GetString("Navn");
string fra = rd.GetString("Fra");
string til = rd.GetString("Til");
items.Add(new praktikanter(praktikant, fra, til));
}
}
}

C# MySql Storing multiple database rows in C#

I'm struggling a bit with this. I want to get the list of ids from the database where a certain value is equal to a certain value in the row. This call will likely return multiple ids. I want to store the value in the ids returned in a list or arraylist in the c# code but I am finding this troublesome. I have the code up to here:
string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
MySqlConnection connection = new MySqlConnection(strConnection);
MySqlCommand command = connection.CreateCommand();
MySqlDataReader reader;
command.CommandText = "SELECT idprojects FROM `test`.`projects` WHERE application_layers = " + applicationTiers + "";
connection.Open();
reader = command.ExecuteReader();
Any help would be much appreciated

string strConnection = ConfigurationSettings.AppSettings["ConnectionString"];
MySqlConnection connection = new MySqlConnection(strConnection);
List<string> array = new List<string>();
using (MySqlCommand cmd = new MySqlCommand("SELECT idprojects FROM `test`.`projects` WHERE application_layers = " + applicationTiers, connection))
{
try
{
using (MySqlDataReader Reader = cmd.ExecuteReader())
{
while (Reader.Read())
{
array.Add(Reader["idprojects"].ToString());
}
}
}
catch (Exception ex)
{
throw;
}
}
string[] ret= array.ToArray();